The size of wireless terminals has been decreasing with many contemporary wireless terminals being less than 11 centimeters in length. Correspondingly, there is increasing interest in small antennas that can be utilized as internally mounted antennas for wireless terminals. Inverted-F antennas, for example, may be well suited for use within the confines of wireless terminals, particularly wireless terminals undergoing miniaturization. Typically, conventional inverted-F antennas include a conductive element that is maintained in a spaced apart relationship with a ground plane. Exemplary inverted-F antennas are described in U.S. Pat. Nos. 6,538,604 and 6,380,905, which are incorporated herein by reference in their entirety.
Furthermore, it may be desirable for a wireless terminal to operate within multiple frequency bands in order to utilize more than one communications system. For example, Global System for Mobile communication (GSM) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. Digital Communications System (DCS) is a digital mobile telephone system that typically operates at high frequency bands, such as between 1710 MHz and 1880 MHz. In addition, global positioning systems (GPS) or Bluetooth systems use frequencies of 1.575 or 2.4-2.48 GHz. The frequency bands allocated for mobile terminals in North America include 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Other frequency bands are used in other jurisdictions. Accordingly, internal antennas are being provided for operation within multiple frequency bands.
Conventionally, PIFA configurations have branched structures such as described in U.S. Pat. No. 5,926,139, and position the PIFA a relatively large distance, typically from about 7-10 mm, from the ground plane to radiate effectively. Kin-Lu Wong, in Planar Antennas for Wireless Communications, Ch. 1, p. 4, (Wiley, January 2003), illustrates some potential radiating top patches for dual-frequency PIFAS. The contents of each of these references are hereby incorporated by reference in their entirety herein. Despite the foregoing, there remains a need for alternative multi-band planar antennas.